Moisture control



March 1, 1955 I 5, sENEY 2,702,948

MOISTURE CONTROL Filed Feb. 12, 1952 3 Sheets-Sheet 1 FIG. 1.

VOLTAGE POWER M g SERVO AMPLIFIER AMPLIFIER MOTOR E (V'5 8V-6) SPEED CONTROL LIMITER ON SLASHER v- 2 PRIMEMOVER SWITCH POWER MULTIVIBRATOR SUPPLY v- I) (v- INVENTOR. JOHN SSE/V5) BY A TT ORNE Y.

March 1, 1955 .1. s. SENEYY MOISTURE CONTROL 3 Sheets-Sheet 2 Filed Feb. 12, 1952 a: INVENTOR.

qomv s. SEA/E) A TTORNE Y.

March 1, 1955 J. 5. SENEY MOISTURE CONTROL 3 Sheets-Sheet 3 Filed Feb. 12, 1952 FIG 0 HEATER EMF ELECTRIC HEATING METAL HEAT TRANSFER SOLUTION SLASHER JOHN S. SENEY ELECTRIC HEATING ELEMENT 2 STAINLESS STEEL A TTORNE) ELECTRODES United States Patent Ofifisce 2,702,948 nherited Mar. 1', 1953 'MOISTURE' CONTROL "John S. Seney, Henrieo *Countyfva assignor 'to EQI.

dn Pont de Nemours and (Company, Wilmington, Del.,

a corporation of Delaware This invention relates to electronic apparatus for controlling the moisture content of a warp of yarns, filaments, ribbons or other continuous textile-material com- .ing from a'drier. More particularly, this invention is concernedwith an electronic controlsystem for regulating the rate of travel of a warp'of yarn ends, bemg dried by passing over a series of drying cans'or drums, as in a slasher, so that the moisture content'of the dried warp is maintained substantially constant.

It has been commonpractice for years'in viscose rayon yarn manufacture to slash-dry yarns destined for use as tire cord reinforcements in order to secure uniformly 'hi'gh tenacity,-uniformly lowelongation and low growth characteristics, and to' be able topackage the yarn production in the-form of beams containing many hundreds of yarn ends. "In-slasher-drying processes, thewarp of .yarn ends is passed through an aqueous finishing and/ or sizing bath, over and around a plurality of heated drying cans and then to the wind-up beam.

In order to present 'a satisfactory product to the customer, the yarn=as it is wound up'on the'beam must con- 'tain no .more'than 12% moisture and preferably be in the range of from 9 to 10% moisture. Even with con trols to maintain each of the drying cans-at a'substantial- 1y constant temperature and with a constant speed drive, moisture in-the yarn at the windup may vary from to 14%. 'Beams of yarn wound with as'much as 14% moisture therein are unsatisfactory and must 'be=rewound. On' the other hand, if the yarn is dried below 9%-mois- -ture for any length of time the rate of production is lower than is desirable. A primary reason for the 'wide variation in moisture content from 5% to 14% is because-it-is not practicable to operate the machine atconstant speed. From time to time breaks occur andthe 'machine must be stopped and started again and again,

disturbing the continuity of operation.

, In my copending application, Serial 'No. 129,250,'filed November 25, 1949, abandoned September 18, 1953, is disclosed amoisture control apparatus adapted to overcome the above difiiculties by measuring the voltage'drop through a travelingwa'rp of yarn, the voltage drop being a function of the moisture content, and regulating the drying operation of the machine accordingly to effect uniform drying. Experience with that apparatus has indicated the desirability of eliminating moving parts insofar as possible in order to reduce maintenance.

It is an object of the present invention to provide an all-electronic apparatus for automatically regulating the rate of travel of continuous textile material through a drier to obtain a uniform moisture content throughout the dried material. Another object is to provide such an apparatus having means to avoid over-correcting for minor moisture deviations while providing for prompt correction of major errors in moisture content. Other objects of the invention will become apparent from the "following description and claims.

In the drawing, which illustrates a preferred embodiment of the invention,

Figure 1 is a block diagram giving a simplified picture of the components of the apparatus and a suggestion of their functions and interaction,

Figure 2 is a complete circuit diagram of the apparatus'of this invention,

Figure 3 is a circuit diagram of a modification of part ofthe apparatus shown in Figure 2, and I Figure 4 is a perspective view of a conductivity compensation electrode assembly.

Figure 1 depicts the electronicsys'ter'nasmade 'u'p'of five 'cornponents,"which-are shown under the respective names of Voltage AmplifienPower Amplifin-Limiter, Switch -Multivibrator, and Power Supply. Interconnections are shown schematically. A wa'r'psheet 10'of 'yarn ends passes from the'slashe'r into contact with two conducting rolls'orguides '11 and'1-2,as indicated diagrammatically at the left of the voltage amplifier to suggest the error input location.

In Figure 2, the two 'conducting'rolls or guideSIIJ'and 12 across which the 'warp sheet'passes 'are' connected'to a'source of-electrical potential. As current flows through the yarn,'which is rendered more conductive by thepresence of moisture; apotential drop between the'i'0lls'niay be observed. This potential difference is applied as input for voltage amplifier tube V-3, which, with-its associated circuitelements makes, -up the voltage amplifier. The difierence betweenthis and aknownvoltage is then amplified. Theoutput fromthe voltageamplifier'goesto the power amplifier, which-produces a corresponding signal of sufficient'power 'to actuate a servomotor Marranged to control the speed of the slasher. Thus, the time during which the yarn dries on the slashers is-arranged to be a function of the amount of moisture prescut.

The slasher may be "any of 'the' conventional equipment used in the art and is not-illustrated. Various methods for adjusting the'slasherspeedarealso conventional. For example, a'suitable means is a positive-infinitely-variable speed changer connected between "the prime mover and the main drive shaft" of the slasherand arranged-to be adjusted; by the servomotor. Since-such speed controls are well-known, this is merely indicated by a block connected to the servomotor by -a dashed line.

The switch multivibrator and "limiter'stages of the system assure prompt response to large moisture fluctuations while also allowing for the drying lag inherent in the slasher system. The operation of these 'components will become understandable from the subsequent description of the wiring diagram, but, in essence, the limiter periodically reduces the output ofthe voltage amplifier to providetime' intervals during which correction can occur only slowly, thus avoiding over-correction when the moisture deviation error ismoderatelysmall.

The switch multivibrator continually turns the limiter on and off in accordance with apredetermined time cycle.

'When the limiter is off, major errors become fully effective, and prompt correction is made for them.

- The power supply transforms the availablepower, such as that furnished by a volt, 60 cycles per sec0nd-line, into the several forms-required to actuate theentire system. As indicated on'Figure 1, there are connections from the power supply to each of the other components.

The operation of the apparatus will now be described with specific reference to Figure 2. The locationofthe components ,therein is similar to the block layout in Figure 1. The power-supply consists of transformer T-3, which is connected to the external power source; tube V-4, which is an ordinary duo-diode rectifier; and resister-capacitor filter elements R16 and 0-9. A manually operated off-on switch S-1 and a fuse F are'present in one of the leads to the powersource. A center-tapped secondary winding of T-3 supplies plate voltage to V-4, which operatesas a full-wave rectifier, providinga pulsating direct voltage at its filament. The output ripple is smoothed by the resistor-capacitor filter, and the ouput is available at point p, from which there are connections to the plate and screen grids of the other tubes at the several points designated pin the diagrams. In addition to the rectifier filament and plate secondaries of T-3, another secondary is present to supply the heating elements of the other tubes. To avoid unduecornplication of the diagram, letters x-and y indicate the appropriate connections from T-3 to these heaters. Theprimaryof transformer T-l is also served by this winding.

Transformer T-1 operates on a relatively low poten tial (6.3 volts). Its secondary is center-tapped and grounded, so that the alternating input potential is split, appearing out ofphase across the secondary terminals. The load across T 1 is primarily resistive, being made: pp of the resistance through'the'warp sheet 10 and an adjustable resistance R-12 added in series with it. A small variable capacitor C7 is connected in parallel with the resistance of the warp sheet, and a similar one, C-8 is across R-12; these are used to assure 180 C. phase opposition of the potential drops through the warp sheet and across R-12 by balancing stray capacitances in the leads and by opposing the inductances of T-l. Midpoint b, between R-12 and the resistance of warp sheet 10, is connected to the grid of tube V-3A, which is a selfcontained one-half of the entire tube V-3, and which amplifies the alternating signal appearing at its grid. Resistor R-10 provides self-bias for V-3A, and R-8 is its plate dropping resistor.

The output from the plate of V-3A is applied to the grid of tube V-3B through coupling capacitor C-3. The amount of amplification may be varied by adjustment of grid resistor R-11, across which the output of V3A appears. Slight amplification is provided by V-3B, Whose plate load is the primary winding of transformer T-2, to which is connected by-pass capacitor C-13. Resistor R-9 provides cathode bias for V-3B, as well as for another tube whose function is set forth below. The center-tapped secondary of T-2 feeds the respective grids of tubes V- and V-6, which are connected cathode-tocathode in the customary manner (called push-pull) as a power amplifier. Resistor R-15 self-biases both V-5 and V-6, while capacitor C-12 between the two grids insures electrical symmetry.

Transformer T-4 matches the load to the power amplifier, receiving the output across a center-tapped winding and capacitor C-2 in parallel and supplying current to one winding of the servo-motor M from a secondary bridged by capacitor C-6. A two-phase induction motor, M has winding L-l energized by the power amplifier output, winding L-2 by the external power source, here the 110 v. 60 cps. line. Switch S2, closed only when the splasher prime mover is operating, is interposed between the external power source and the line winding of M to prevent unnecessary or unsafe operation of the servo mechanism. The currents through the two windings of the servo-motor M are in quadrature so that they set up a rotating magnetic field, which drives the motor. Since the peak value of the alternating current through the line winding L-2 of M does not vary, the peak value of the power amplifier output current through winding L-l determines the speed of rotation. If there is no output, the motor will not run. In this way, the degree of moisture deviation from a standard (represented by the setting of R-12) determines the amount of speed correction applied to the slasher.

To follow the method by which M senses the direction of the deviation, the instantaneous value of the alternating potential must be examined. Assume the presence of too much moisture; then the resistance across the warp sheet will be smaller than that across R-12.

Consequently, when point x is at the peak positive potential with respect to point y, point b is slightly positive with respect to ground. One quarter cycle later, all these points are at ground potential; one-quarter cycle after that, point b is as much negative as it formerly was positive. Had the yarn been too dry, this alternation in potential at point b would have been just the opposite: b being negative when x is positive, positive when x is negative. Such an opposition in the potential alternation would appear at the power amplifier output and cause a reversal of the rotating magnetic field of M, thus reversing the direction in which the rotor of M is turning. Accordingly, M is connected so that the slasher speed is increased when the warp is too dry and is decreased when more evaporation is desired.

To allow for the time lag present in a slasher type of drying operation, a limiter tube V-2 is included. When V-2 is conducting, current flowing through it (which is considerably greater than the normal flow through V-3B) passes through resistor R-9, which is a common cathodebias resistor for V-2 and V-3B. This causes a rise in potential of the cathode of V-3B, as well as that of V2, imposing further bias upon V-3B and thus decreasing its output. This diminution of error signal provides for a lag in the response of the servo-motor M to avoid overcorrecting for minor discrepancies in the moisture condition, such as transient fluctuations. However, if V-Z conducted all the time, the lag would become too great, so it is turned off at intervals by the switch multivibrator. This switching action permits prompt correction of ma or errors during the time when V-2 is non-conducting. It should also be noted that a very large error signal at the grid of V-3 Will be effective in spite of the bias imposed by a conducting V-2.

The switch multivibrator is free-running; that is, no trigger is required to provoke the switch action. This component consists of tubes V-lA and VlB, here shown in one envelope. The grid of each is coupled to the plate of the other by a capacitor. Each capacitor and its associated grid resistor together govern the period of conduction of the tube to whose plate the capacitor is connected. The operation may be understood by considering the circuit at a particular time.

Assume that tube V-lA is conducting. When the surge of plate current began earlier in V-lA, a potential drop developed across its plate resistor R3. Coupling capacitor C-l has one side tied to this plate, so it is always at the plate potential. Since an appreciable time is required for a change in potential to develop between the plates of a capacitor, the opposite side of C-1 also suffered a decrease in potential when V-lA began to conduct. However, the slight positive potential of this side of C-1 which is separated from ground by the grid resistors R-1 and R-13 of V1B, was replaced by a large negative potential at that time. This fall in potential at the grid of V1B insured cut-otf; no plate current could pass through it when so strongly biased.

In time, however, the negative charge on the grid side of C-1 leaks off to ground through R-1 and R-13. As its grid potential rises, V-1B eventually starts to conduct. When that happens, its plate potential falls, coupling a negative impulse to the grid of V-lA which reduces current flow through V1A. The plate potential of V-1A then rises, giving a positive impulse to the grid of V-1B, further increasing its plate current. This cumulative action is very rapid, so that for most purposes it may be thought of as an instantaneous switching oil of one tube and turning on of the other. The converse of this action occurs a short while later, after the negative charge on the grid capacitor C-4 of V-1A has leaked to ground through grid resistors R-2 and R14 suificiently to permit V1A to conduct once more.

The periodicity of the switching is controlled by the time constants of the respective grid circuits. If the adjustable grid resistors are set nearly equal, the time constant of the V-1B grid circuit will be much larger than that for V-1A because C-l is ten times as large as C-4. This will cause V1B to be cut ofi much more than the normally conducting V-1A. As the plate potential of V-lB falls during conduction and rises upon cut-off, the grid of V-Z receives a negative and then a positive pulse through its coupling capacitor C-S. Since V-lB is normally non-conducting, V-2 is normally conducting, limiting the amplification of the error signal. Alteration of the time constants in the V-1 circuits will change the period during which V2 conducts, thus varying the degree of control that the apparatus exerts upon the servo system. The time cycle is adjusted to provide for adequate correction of major errors during the time the limiter is inoperative but, on the other hand, to maintain the limiter in operation for sufficient time to avoid overcorrection for minor errors.

As a refinement of the apparatus to permit a wider ran e of correction speed, a direct potential that is indicative of the slasher speed may be inserted in the multivibrator circuit in such a Way as to alter the ratio of the conductive periods of V-lA and V-lB. In this way, the correction lag can be increased greatly for slow-speed operation of the warp transporting equipment, and decreased sharply for high-speed operation. This may be accomplished by injection of the speed-dependent bias in the plate circuit of V-1A at the point marked g on Figure 2, for example. At higher speeds of slasher operation the conducting period of V-lA should be de creased with respect to the conducting period of V-IB, thus decreasing the non-conducting time of V-2 with respect to its conducting time in order to allow the full amplification of the error signal present at the grid of V-3B to pass on to the power amplifier for more rapid correcting action. This can be accomplished simply by separating the plate lead of V-lA at point g and inserting the slasher rate-dependent potential with polarity such that the lead from the positive connection goes to R-5, and the negative lead to R-3. The bias inserted here may be produced by a simple tachometer generator driven from the slasher itself. Other types of speed-responsive electrical generating devices may be used, as will be apparent to those skilled in the art. No generator itself is shown in Figure 2, as the above description and general knowledge of slasher operation are sufficient for .a complete understanding of the construction and operation of this refinement of the apparatus.

Although the apparatus of this invention as shown in Figure 2 has been described as operating with-an alternating potential applied across the warp sheet whose resistance (and therefore moisture content) is being measured, satisfactory operation from a battery or other source of directpotential is permissible by utilizing the modification shown in Figure 3. By inserting the circuit diagram of Figure 3 in place of that portion of Figure 2 enclosed by dashed lines, conversion tooperation with direct potential to establish the potential drop across the warp sheet is accomplished. Figure 3 depicts also a stage of pre-amplification useful when this mode of operation is selected.

Figure 3 repeats the showing of warp sheet between conducting guides or rolls'll and 12 connected respectively to points b and a.

Direct potential supplied by battery B-l appears across resistor R-102 whose slider arm connects at point a. A lead from the positive end of the battery connects with the vibrating arm of converter CONV, which is actuated by the same alternating potential that supplies the tube filaments, as shown by indicated connections x and y to the converter coil. The contacts of the converter are connected to opposite ends of the primary of transformer T-101, from which a center tap leads back to the warp sheet through the series combination of galvanorneter G, a portion of the slider of resistor R112, and resistor R-119. Battery B-2 supplies a small balancing potential across resistor R-112 so that the fraction picked off by the slider of R-102 and appearing across R104 is equal and opposite to that across R-103 when the moisture content of the warp sheet is at the desired value. In this respect R-llZ of this modification corresponds to R-lZ of Figure 2, being set at a value to provide zero error signal when the optimum moisture is present in the warp sheet. Capacitor C111 prevents entrance of stray alternating signals that may be present outside the amplification system. As the vibrator establishes paths for current flow alternately through halves of the split primary of T-101, the potential induced in the secondary alternates rapidly and uniformly with a peak-to-peak magnitude dependent upon the size of the potential drop through the warp sheet. The variation in phase and magnitude of the signal across the secondary of T-101 in this modification is related to the warp sheet moisture just as is the varying signal present across the secondary of T-1 and its parallel circuit elements in Figure 2.

The alternating error signal appears at the grid of V-7 across resistor R115 in parallel with the secondary 101. Cathode bias for V-7 is provided by resistor R-l16 by-passed by capacitor C108. Resistors R-117 and R-llS act as plate dropping resistors, and capacitor 0-109 improves the filtering action. The amplified alternating signal present at the plate of V-7 is coupled through capacitor C-110 to appear across resistor R-114 at point c, which is at the grid of V-3A as shown in Figure 2.

Neither the circuit enclosed by dashes in Figure 2 nor the circuit of Figure 3 is necessary to the operation of the rest of the apparatus; any equivalent circuit that will provide an alternating signal indicative of the resistance of the warp sheet may be fed in at point 0 to provide the desired impulse to control the slasher speed. The resistance across the warp sheet may be replaced by the cathode resistance of a relaxation oscillator tube whose plate circuit contains as one of its elements the resistance across the warp sheet, as shown in my co-pending application Serial No. 271,262, filed February 12, 1952. Obviously, in such an arrangement, the short-time average cathode current through the tube is dependent upon the resistance across the warp sheet. Such cathode resistance might be inserted across points b and a of Figure 3 to replace elements 10, 11, 12, B.l and R-102. Connecting points 12 and a are shown on Figure 2 of my co-pending application Serial No. 271,262. Other usefulmethods of obtaining a potential drop suitable for actuating the apparatus of this invention will be apparent to those skilled in the art.

As a further refinement of this apparatus, a potential this purpose. interposed'between the electrodes and points a andjrif the measurement.

heating elements 20 and 21 inside conducting ltion employed in the slasher may be' injected.;in such a way -as tominimizethe. effect of deviations in conductivity of the .size. This improvement may be accomplished simply by connecting to each of points a-and .f {(shown in Figure 3) electrodes immersed in the sizing solution. Figure 4 shows a pair-of electrodes usedrfor A conductivity measuring circuit maybe desired.

Many kinds of sizing solutions normally employed in slashing synthetic yarns contain-materials,.such as waxes or resins, that may deposit on the conductivity'electrodes to produce a high-resistance coating that interferes with This difficulty may be overcome most successfully by using heating elements inside eachelecnode as shown in Figure 4. The temperature required to prevent interfering materials fromdepositing on t-he electrode surfaces may be ascertained by visual observation of the surfaces and'by routine calibration of the instrument. Other. refinements for improving the 'accuracy of the apparatus 'of' this invention will be apparent.

-In Figure 4, leads h, -h connect to a source of potential, hich may be furnished by the power supply, to operate sheaths-or electrodes 22 and 23 mounted upon an insulating block 24. It is desirable for at least one of the heating elements to have associated with it a control device to keep the temperature within close limits. Also shown in Figure 4 is a metal block 25 surrounding electrode 23 and mounted on insulator 24 to conduct heat from the electrode to a thermostatic control element 26 inside tube 27, from which protrudes adjusting rod 28. Construction of the temperature-sensitive and switch portions of the control are not critical, and any of many constructions well known in temperature control art may be employed.

Since many different embodiments of the invention may be made without departing from the spirit and scope thereof, it is to be understood that the invention is not limited by the specific illustration except to the extent defined in the following claims.

What is claimed is:

1. In an apparatus for conveying textile material through a drying zone, electrical means for measuring the moisture content of said material comprising an amplifier responsive to differences of phase and magnitude between potential drops existing across a portion of said material forming an element of said amplifier and across a standard resistor, and a limiter network for periodically limiting the amplification of said'ditierences as accomplished by said amplifier; and means for controlling the rate at which said material is conveyed through the drying zone in accordance with the measured moisture content comprising a control circuit including a servomotor actuated by said comparison circuit and means for varying said conveying rate operated by said servo-motor.

2. In an apparatus for conveying textile material through a drying zone, electrical means for measuring the moisture content of said material comprising a voltage amplifier including sensing elements in contact with a portion of said material for producing an error signal corresponding to the deviation of the potential drop created across said portion from the potential drop existing across a reference resistor in said voltage amplifier, a limiter for reducing the amplification accomplished by said voltage amplifier, and a switching circuit to render said limiter alternately effective and ineffective in reducing said amplification, and means for controlling the rate at which said material is conveyed through the drying zone in accordance with the measured moisture content compris' ing a power amplifier for increasing the power level of the amplified signal produced by said voltage amplifier, a servo-motor actuated by said power amplifier, and means for varying said conveying rate operated by said servomotor.

3. In an apparatus for conveying textile material through a drying zone, electrical means for measuring the moisture content of said material comprising a transformer having a primary connected to a source of alternating potential and a center-tapped secondary across which are connected in series a portion of said material and a reference resistor, each having associated in parallel with it a separate compensating capacitor, a voltage amplifier including at least two electronic amplifying tube components connected in cascade, the control grid of the first of said components being connected to the junction of the series connection of said resistor and said material, a limiter tube having at least a cathode and an anode and a grid, said cathode being connected to the cathode of a cathode-biased tube component of said voltage amplifier, and a self-triggering switch multivibrator circuit whose output is applied to the grid of said limiter tube to render it alternately active and inactive in reducing the amplification of said voltage amplifier; and means for controlling the rate at which said material is conveyed through the drying zone in accordance with the measured moisture content comprising a power amplifier connected to the plate circuit of said voltage amplifier, and responsive to the output of said voltage amplifier, a transformer for applying the output of said power amplifier to a servo-motor, and a servo circuit including said servomotor responsive to the output of said power amplifier and operative to control said apparatus.

4. In a circuit adapted to control a variable physical condition in response to an electrical error signal derived by continuous sampling of material moving past a fixed sampling point and indicative of deviation of said condition from a desired value, the combination of amplifier means for magnifying said error signal, limiter means 25 operable to reduce the magnification of said error signal by said amplifier means, repeating switch means for controlling operation of said limiter means, said switch means including means for interrupting operation of said limiter means periodically in accordance with a predetermined time cycle and for varying the proportion of time the operation is interrupted in accordance with rate of movement of said material being sampled.

5. The apparatus of claim 4 in which the switch means includes a multivibrator circuit for interrupting operation of the limiter means periodically in accordance with the switching period of the multivibrator.

6. The apparatus of claim 5 in which the switching period of the multivibrator varies in accordance with a potential dependent upon the sampling rate and injected at one element of the multivibrator.

References Cited in the file of this patent UNITED STATES PATENTS 2,244,722 Norcross June 10, 1941 2,300,999 Williams Nov. 3, 1942 2,346,437 Krogh Apr. 11, 1944 2,535,930 Jones Dec. 26, 1950 FOREIGN PATENTS 636,092 Great Britain Apr. 19, 1950 

1. IN AN APPARATUS FOR CONVEYING TEXTILE MATERIAL THROUGH A DRYING ZONE, ELECTRICAL MEANS FOR MEASURING THE MOISTURE CONTENT OF SAID MATERIAL COMPRISING AN AMPLIFIER RESPONSIVE TO DIFFERENCES OF PHASE AND MAGNITUDE BETWEEN POTENTIAL DROPS EXISTING ACROSS A PORTION OF SAID MATERIAL FORMING AN ELEMENT OF SAID AMPLIFER AND ACROSS A STANDARD RESISTOR, AND A LIMITER NETWORK FOR PERIODICALLY LIMITING THE AMPLIFICATION OF SAID DIFFERENCES AS ACCOMPLISHED BY SAID AMPLIFIER; AND MEANS FOR CONTROLLING THE RATE AT WHICH SAID MATERIAL IS CONVEYED THROUGH THE DRYING ZONE IN ACCORDANCE WITH THE MEASURED MOISTURE CONTENT COMPRISING A CONTROL CIRCUIT INCLUDING A SERVOMOTOR ACTUATED BY SAID COMPARISON CIRCUIT AND MEANS FOR VARYING SAID CONVEYING RATE OPERATED BY SAID SERVO-MOTOR. 